The use of optical fibers is becoming increasingly more popular in many industries. Predominant among them is the use of optical fibers in the communication industry. Large amounts of information can be transmitted more efficiently over optical fibers than with electrical transmission through conventional electrically conductive wires.
One technical consideration of the use of optical fibers not present in conventional metal wire conductors is the fact that, when interconnected, it is necessary to align optical fibers in a serial, substantially coaxial and abutting relationship. Many techniques and devices exist to satisfy the requirements for interconnection of optical fibers. Among those are cementing or gluing the end of each fiber to a holder and then aligning the fiber ends secured by those holders within a connector. As it is often desirable to secure the fibers quickly, fast-setting cements and adhesives have been employed for this purpose. Often, however, cyano-acrylic adhesives or other fast-setting cements react chemically with the glass fiber whereby optical transmission loss can occur. Likewise, epoxies, a slower setting class of adhesives, may also involve chemical attack. In order to prevent these deleterious chemical effects, mechanical clamping devices have been recommended. However, mechanical clamping may lead to destruction of optical fibers or often induce local stresses within the fiber itself thereby distorting and degrading the light transmission through the fiber.
In order to more fully comprehend the nature of optical fibers and the requirements for an interconnector therefor, it is necessary to briefly describe conventional manufacturing methods of single-mode optical fibers. Generally, a single-mode optical fiber is created from optical fiber quality glass tubes of 5/8-inch to 1/4-inch diameter. These tubes are placed on a lathe and heated with a torch. While undergoing heating, certain gasses such as argon are pumped into the interior of the tube and coat the entire interior surface thereof. As the temperature rises, the tube collapses to become a solid rod which, while molten, is then pulled in the direction of elongation to form a 125 diameter micron thread. The optically transmittive core section, that which includes the residual gas which initially adhered to the interior surface of the tube, has a diameter of approximately 6 index of refraction due to the noble gas coating while the surrounding glass, commonly referred to as the armor, has a high index of refraction.
When drawing the fiber from the molten tube, many forces, i.e., gravity, torque, etc., affect the relative position of the core within the fiber cross section. Thus, merely aligning the optical fibers end-to-end, in a substantially coaxial relationship does not necessarily create maximum transmission through the intersection of joined optical fibers. Indeed, imperfect alignment of the optical cores by more than half a micron, will result in a substantial amount of light transmission loss.
Now turning to the physical aspects of optical fibers, it first should be noted that optical fibers are so fragile that if unshielded, a fiber will shatter upon contact with another. In view of the fragile nature of optical fibers, as well as the necessity for proper connection, great efforts have been expended to overcome the problems associated with interconnection. Conventionally, fibers are coated in a plastic sheath, excepting the ends. The fiber ends then are placed in a holder, usually polymeric, and cemented thereto. When so glued, two holders are then aligned within a connector and cemented with quick-setting adhesives. Often, cyano-arcylic adhesives are employed for this purpose. However, cyano-acrylic adhesives suffer from the above noted shortcoming of chemically reacting with glass fibers and, therefore, generate flaws in the optical fibers and a corresponding loss of optical transmission capacity. Where slower setting epoxies are selected for cementing the holders, similar chemical attack on the fiber may occur due to the hardener, catalyst or other components. Furthermore, the initial alignment of the optical fiber ends may not be preserved due to the necessary setting time and, therefore, an even greater loss of transmission efficiency may occur.
Less common, but also used, are various mechanical clamping devices to secure the fiber ends in an optically transmittive relationship to each other. Mechanical clamping, however, suffers from the shortcoming of subjecting the optical fiber to localized stress which distorts the fiber which again leads to degradation of the light transmission properties of the fiber. Furthermore, in the event too much force is applied in a mechanical clamping context, the fibers will shatter.